[wastedyears]

After firing a machine gun, some of them will want to buy one.

If they have a Class III license, $20,000 for the automatic, and the money to feed it, as well as the $200 for the tax stamp.

[mylife]

Bumpfire systems now offers a $99 solution, but you still need to feed it.

https://www.bumpfiresystems.com/

[backwoods-engineer]

If they have a Class III license,

An SOT is not required, in fact. If you live in a free state, just the tax stamp, the $200, and and patience to wait. Well, and fingerprints in triplicate.